Nonaqueous electrolyte secondary battery and cathode sheet therefor

ABSTRACT

The invention provides a cathode sheet for use in a nonaqueous electrolyte secondary battery, including a composite material comprising a collector and a layer of a cathode active material provided thereon. The layer of a cathode active material includes: (a) a conductive polymer and (b) at least one selected from a polycarboxylic acid and a metal salt of a polycarboxylic acid; and the conductive polymer is a polymer in a dedoped state or in a dedoped and reduced state. The polymer constituting the conductive polymer is at least one selected from polyaniline, a polyaniline derivative, polypyrrole, a polypyrrole derivative, and polythiophene; and the polycarboxylic acid is at least one selected from polyacrylic acid, polymethacrylic acid, polyvinylbenzoic acid, polyallylbenzoic acid, polymethallylbenzoic acid, polymaleic acid, polyfumaric acid, polyglutaminic acid, polyaspartic acid, alginic acid, carboxymethylcellulose, and a copolymer including repeating units of at least two of the polymers listed herein.

This application continuation of application Ser. No. 14/129,639, filedApr. 11, 2014, which is a National Stage of International ApplicationNo. PCT/JP2012/067032, filed on Jun. 27, 2012, which claims priorityfrom Japanese Patent Application Nos. 2011-143690, filed on Jun. 29,2011, and 2012-084921, filed on Apr. 3, 2012, the contents of all ofwhich are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a nonaqueous electrolyte secondarybattery and a cathode sheet therefor. More particularly, the inventionrelates to a nonaqueous electrolyte secondary battery, preferably alithium secondary battery, which is superior in weight energy densityand weight power density, and in addition, in cycle characteristics. Theinvention further relates to a cathode sheet for use in the nonaqueouselectrolyte secondary battery.

BACKGROUND ART

With the progress and advance of electronics in the fields of portablepersonal computers, mobile phones, and personal digital assistances(PDA) in recent years, a secondary battery which can be repeatedlycharged and discharged is in wide use as an electric storage device forthese electronic devices.

Among the secondary batteries, the so-called rocking chair type lithiumion secondary battery is particularly in wide use as an electric storagedevice for such electronic devices as mentioned above because of thereasons as follows. The so-called rocking chair type lithium ionsecondary battery uses as an active material a lithium-containingtransition metal oxide such as lithium manganate or lithium cobaltatefor a cathode and a carbon material into which lithium ions can beinserted and from which lithium ions are extracted for an anode so thatwhile it is charged and discharged, the lithium ion concentration in theelectrolytic solution does not substantially change. Thus, the rockingchair type lithium ion secondary battery needs electrolytic solution inan amount smaller than the so-called reserve type secondary battery.Such being the case, the rocking chair type lithium ion secondarybattery can be downsized more readily than the reserve type secondarybattery. Furthermore, the rocking chair type lithium ion secondarybattery has a high energy density.

However, the lithium ion secondary battery is an electric storage devicewhich obtains electric energy by electrochemical reactions. Thus, it hasa material problem that it has a low power density because the rate ofthe electrochemical reactions is small. In addition, because the lithiumion secondary battery has a high internal resistance, it can be hardlycharged and discharged rapidly.

Besides, as the lithium ion secondary battery contains a cathode activematerial having a large specific gravity, it leaves room for improvementof capacity density per unit weight, and on the other hand, as theelectrode and electrolytic solution deteriorate due to electrochemicalreactions when the battery is charged and discharged, it has aninsufficient life, or cycle characteristics.

Under these circumstances, a nonaqueous electrolyte secondary battery inwhich a conductive polymer such as polyaniline having a dopant is usedas a cathode active material is already known (see Patent Document 1).

However, in general, a nonaqueous electrolyte secondary battery whichcomprises a conductive polymer as a cathode active material cannotcontribute to downsizing of a secondary battery. The reason is thatbecause the nonaqueous electrolyte secondary battery which comprises aconductive polymer as a cathode active material is an anion-migratingtype battery in which the conductive polymer is doped with anions whenthe battery is charged, and the anions are dedoped from the polymer whenthe battery is discharged, a rocking chair type secondary battery cannotbe constructed when a carbon material is used as an anode activematerial into which lithium ions are inserted and from which lithiumions are extracted, and hence the battery needs a large amount ofelectrolytic solution.

In order to solve the problem mentioned above, a cation-migrating typesecondary battery in which a cathode is formed of a conductive polymerhaving polymer anions such as polyvinylsulfonic acid as a dopant so thatthe ion concentration in the electrolytic solution remains substantiallyunchanged is proposed (see Patent Document 2). But the batteryperformance is not yet sufficient.

On the other hand, in recent years, a strategy for solving a problem ofair pollution and, even a strategy for solving a problem of globalwarming, are earnestly studied. As one of the strategies, a hybridvehicle and an electric vehicle have already reached a stage ofpractical use, and a lithium ion secondary battery has been put topractical use in part as an electric storage device for such vehicles.

However, although an electric storage device for hybrid or electricvehicles is required to have a high power density in particular when itis rapidly charged through a process of generative brake, or when avehicle is accelerated, a lithium ion secondary battery has a highenergy density, but it has a problem of low power density, as set outhereinbefore.

An electric double layer capacitor thus attracts attention. The electricdouble layer capacitor is an electric storage device which uses apolarizable electrode usually formed of a conductive and porous carbonmaterial having a large specific surface area such as powder charcoaland fibrous charcoal, and which makes use of physical adsorptioncharacteristics of supporting electrolyte ions in electrolytic solution.Therefore, the electric double layer capacitor has a high power densityand is capable of being charged rapidly, and besides it has a very longlife. However, on the other hand, as it has an energy density muchsmaller than a lithium ion secondary battery, it is problematic if theelectric double layer capacitor can be put to practical use as anelectric storage device for hybrid or electric vehicles.

For example, the electric double layer capacitor has a cycle life about10-100 times longer, and a power density about 5 times larger, than alithium ion secondary battery; however, the electric double layercapacitor has a weight energy density about 1/10-½ as much as a lithiumion secondary battery, and a volume energy density about 1/50- 1/20 asmuch as a lithium ion secondary battery (see Patent Document 3).

PRIOR ART DOCUMENTS Patent Documents Patent Document 1: JP 3-129679 APatent Document 2: JP 1-132052 A Patent Document 3: JP 2008-16446 ASUMMARY OF THE INVENTION Problems to be Solved by the Invention

The invention has been made to solve the above-mentioned problemsinvolved in the conventional electric storage devices such as secondarybatteries and electric double layer capacitors. Therefore, it is anobject of the invention to provide a novel nonaqueous electrolytesecondary battery which is superior in weight power density and cyclecharacteristics like an electric double layer capacitor, and which hason the other hand a weight energy density much higher than that ofconventional electric double layer capacitors. It is a further object ofthe invention to provide a cathode sheet for use in the nonaqueouselectrolyte secondary battery mentioned above.

Means for Solving the Problems

The invention provides a nonaqueous electrolyte secondary battery havinga cathode and an anode arranged so as to be opposite to each other, andan electrolyte layer put therebetween;

wherein the cathode comprises:

-   -   (a) a conductive polymer and    -   (b) at least one selected from the group consisting of a        polycarboxylic acid and a metal salt thereof, and

wherein the anode comprises a material into which a base metal or ionsthereof can be inserted and from which a base metal or ions thereof canbe extracted.

The invention further provides a cathode sheet for use in the nonaqueouselectrolyte secondary battery, which comprises a composite materialcomprising a collector and a layer of a cathode active material providedthereon,

wherein the cathode active material comprises:

-   -   (a) a conductive polymer and    -   (b) at least one selected from the group consisting of a        polycarboxylic acid and a metal salt thereof.

According to the invention, the nonaqueous electrolyte secondary batteryis preferably a lithium secondary battery, and therefore the cathodesheet for use in the nonaqueous electrolyte secondary battery ispreferably a cathode sheet for use in the lithium secondary battery.

Effect of the Invention

The nonaqueous electrolyte secondary battery of the invention issuperior in weight power density and cycle characteristics as if it wasan electric double layer capacitor, and besides it has a weight energydensity much higher than that of conventional electric double layercapacitors. That is, the nonaqueous electrolyte secondary battery of theinvention is a secondary battery having the performance like that of acapacitor.

Further, the nonaqueous electrolyte secondary battery of the inventionwhich is obtained by using the cathode sheet of the invention as well asa material into which a base metal or ions thereof can be inserted andfrom which a base metal or ions thereof can be extracted as an anode issuperior in weight power density and cycle characteristics like anelectric double layer capacitor, and in addition, it has a weight energydensity much higher than that of conventional electric double layercapacitors.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is an FT-IR spectrum of conductive polyaniline powder havingtetrafluoroborate anions as a dopant;

FIG. 2 is an ESCA spectrum (wide scan) of the above-mentioned conductivepolyaniline powder;

FIG. 3 is a scanning electron micrograph magnified 20000 times of theabove-mentioned conductive polyaniline powder;

FIG. 4 is a graph showing the relation between the cycle number andweight capacity density obtained when an example of the lithiumsecondary battery of the invention of which cathode comprises aconductive polyaniline having tetrafluoroborate anions as a dopant ischarged and discharged;

FIG. 5 is a graph showing the relation between the cycle number andweight energy density obtained when the above-mentioned example of thelithium secondary battery of the invention is charged and discharged;

FIG. 6 is a graph (charge/discharge curve) showing the relation betweenthe weight capacity density and voltage obtained when theabove-mentioned example of the lithium secondary battery of theinvention is charged and discharged at various rates;

FIG. 7 is a graph showing the relation between the charge/dischargecycles and energy density retention obtained when the above-mentionedexample of the lithium secondary battery of the invention is charged anddischarged at a rate as high as 8.3 C;

FIG. 8 is a graph showing the relation between the charge/discharge rateand weight energy density of the above-mentioned example of the lithiumsecondary battery of the invention and a lithium secondary battery as acomparative example;

FIG. 9 is a graph showing the relation between the cycle number andweight capacity density obtained when a second example of the lithiumsecondary battery of the invention of which cathode comprises aconductive polyaniline having tetrafluoroborate anions as a dopant ischarged and discharged;

FIG. 10 is an FT-IR spectrum of reduced and dedoped polyaniline powderobtained by neutralizing a conductive polyaniline havingtetrafluoroborate anions as a dopant, and then by reducing the resultingpolyaniline;

FIG. 11 is a graph showing the relation between the cycle number andweight capacity density obtained when an example of the lithiumsecondary battery of the invention of which cathode comprises thereduced and dedoped polyaniline powder mentioned above is charged anddischarged;

FIG. 12 is a graph showing the relation between the cycle number andweight energy density obtained when the above-mentioned example of thelithium secondary battery of the invention is charged and discharged;

FIG. 13 is an FT-IR spectrum of a conductive poly(o-toluidine) powderhaving tetrafluoroborate anions as a dopant;

FIG. 14 is a graph showing the relation between the cycle number andweight capacity density obtained when the above-mentioned example of thelithium secondary battery of the invention of which cathode comprises aconductive poly(o-toluidine) powder having tetrafluoroborate anions as adopant is charged and discharged;

FIG. 15 is a graph showing the relation between cycle number and weightenergy density obtained when the above-mentioned example of the lithiumsecondary battery of the invention is charged and discharged;

FIG. 16 is a graph showing the relation between the charge/dischargecycle number and weight capacity density obtained when theabove-mentioned example of the lithium secondary battery of theinvention is discharged at a constant current;

FIG. 17 is a graph showing the relation between the charge/dischargecycle number and weight energy density obtained when the above-mentionedexample of the lithium secondary battery of the invention is dischargedat a constant current;

FIG. 18 is an FT-IR spectrum of a conductive polypyrrole powder havinganthraquinone-2-sulfonate anions as a dopant;

FIG. 19 is a graph showing the process of initial activation of anexample of the lithium secondary battery of the invention of whichcathode comprises a conductive polypyrrole havinganthraquinone-2-sulfonate anions as a dopant;

FIG. 20 is a graph showing the rate characteristics of theabove-mentioned lithium secondary battery of the invention;

FIG. 21 is a graph showing the relation between the charge/dischargecycle number and weight capacity density of the above-mentioned lithiumsecondary battery of the invention;

FIG. 22 is a TEM image of reduced and dedoped polyaniline after it hasbeen stained with ruthenic acid;

FIG. 23 is a TEM image of a section parallel to the surface of a cathodesheet comprising conductive polyaniline;

FIG. 24 is an FT-IR spectrum of a reduced and dedoped poly(o-toluidine)powder (KBr disk);

FIG. 25 is a graph showing the relation between the cycle number andweight capacity density obtained when an example of the lithiumsecondary battery of the invention of which cathode comprises thereduced and dedoped poly(o-toluidine) powder mentioned above is chargedand discharged; and

FIG. 26 is a graph showing the results of rate tests of a lithiumsecondary battery as a comparative example which is provided with acathode sheet comprising a binder composed of a mixture ofstyrene-butadiene copolymer rubber and poly(N-vinylpyrrolidone),together with a reduced and dedoped polyaniline.

EMBODIMENTS OF THE INVENTION

The nonaqueous electrolyte secondary battery of the invention has acathode and an anode arranged so as to be opposite to each other, and anelectrolyte layer put therebetween;

wherein the cathode comprises:

-   -   (a) a conductive polymer and    -   (b) at least one selected from the group consisting of a        polycarboxylic acid and a metal salt thereof, and

wherein the anode comprises a material into which a base metal or ionsthereof can be inserted and from which a base metal or ions thereof canbe extracted.

The cathode sheet of the invention for use in the nonaqueous electrolytesecondary battery comprises a composite material comprising a collectorand a layer of a cathode active material provided thereon,

wherein the cathode active material comprises:

-   -   (a) a conductive polymer and    -   (b) at least one selected from the group consisting of a        polycarboxylic acid and a metal salt thereof.

Herein the invention, the conductive polymer means a group of polymerssuch that they change their conductivity when ion species are insertedthereinto or ion species are extracted therefrom so that the change ofelectric charge generated or eliminated by oxidation reaction orreduction reaction of main chains of polymer is compensated. When ionspecies are inserted into a polymer, and as a result, the polymer has ahigh conductivity, then the polymer is said to be in a doped state, andwhen ion species are eliminated from a polymer, and as a result, thepolymer has a low conductivity, then the polymer is said to be in adedoped state.

If a conductive polymer loses its conductivity on account of oxidationor reduction reaction to become insulative (i.e., dedopoed), theinsulative polymer can reversibly become conductive again byoxidation/reduction reaction. Thus, herein the invention, such a polymerin an insulative state also falls under the category of conductivepolymers.

Therefore, according to the invention, one of preferred conductivepolymers is a polymer which has as a dopant at least one protonic acidanions selected from the group consisting of inorganic acid anions,aliphatic sulfonic acid anions, aromatic sulfonic acid anions, polymersulfonic acid anions and polyvinylsulfuric acid anions. Another one ofpreferred conductive polymers is a polymer in a dedoped state which isobtained by dedoping the above-mentioned conductive polymer.

In the invention, the polycarboxylic acid is a polymer that hascarboxylic groups in the molecule. The polycarboxylic acid is preferablyat least one selected from the group consisting of polyacrylic acid,polymethacrylic acid, polyvinylbenzoic acid, polyallylbenzoic acid,polymethallylbenzoic acid, polymaleic acid, polyfumaric acid,polyglutaminic acid, polyaspartic acid, alginic acid,carboxymethylcellulose, and a copolymer comprising repeating units of atleast two of the polymers listed herein. Herein the invention, thecopolymer includes a graft copolymer.

In the invention, the metal salt of the polycarboxylic acid is at leastone selected from the group consisting of an alkali metal salt and analkaline earth metal salt. The alkali metal salt is preferably a lithiumsalt and a sodium salt, and the alkaline earth metal salt is preferablya magnesium salt and a calcium salt.

According to the invention, the polymer that provides a conductivepolymer includes, for example, polypyrrole, polyaniline, polythiophene,polyfuran, polyselenophene, polyisothianaphthene, polyphenylenesulfide,polyphenyleneoxide, polyazulene, poly(3,4-ethylenedioxythiophene),polyacene, and various derivatives of these polymers. Among thesepolymers, one of preferred polymers is at least one selected from thegroup consisting of polyaniline and derivatives thereof because theyhave a large capacity per unit weight.

According to the invention, the polyaniline is a polymer obtained byelectrochemical polymerization or by chemical oxidation polymerizationof aniline, and the derivative of polyaniline is a polymer obtained byelectrochemical polymerization or by chemical oxidation polymerizationof a derivative of aniline. There may be mentioned as examples of thederivative of aniline, for example, an aniline which has at least onesubstituent selected from the group consisting of an alkyl group, analkenyl groups, an alkoxy group, an aryl group, an aryloxy group, analkyl aryl group, an aryl alkyl group, and an alkoxyalkyl group at aposition except the 4-position of aniline.

Preferred examples of the derivative of aniline include o-substitutedanilines such as o-methyl aniline, o-ethyl aniline, o-phenylaniline,o-methoxy-aniline, and o-ethoxyaniline, and m-substituted anilines suchas m-methyl aniline, m-ethyl aniline, m-methoxy aniline,m-ethoxyaniline, and m-phenylaniline.

However, according to the invention, among the detivatives of anilinehaving a substituent at the 4-position, p-phenylaminoaniline can beexceptionally used as a derivative of aniline because it providespolyaniline by oxidation polymerization.

According to the invention, among the polymers that provide conductivepolymers, a second preferred polymer is at least one selected from thegroup consisting of polypyrrole and derivatives thereof because theirrepeating unit has a formula weight as small as 65.08 so that theypossibly have a high capacity density per unit weight.

In the invention, polypyrrole means a polymer obtained by chemicaloxidation polymerization or electrochemical oxidation polymerization ofpyrrole, and a derivative of polypyrrole means a polymer obtained bychemical oxidation polymerization or electrochemical oxidationpolymerization of a derivative of pyrrole. There may be mentioned asexamples of the derivative of pyrrole, for example, a pyrrole which hasat least one substituent selected from the group consisting of an alkylgroup, an alkenyl group, an alkoxy group, an aryl group, an aryloxygroup, an alkyl aryl group, an aryl alkyl group, and an alkoxyalkylgroup at a position except the 2- and 5-position.

Preferred examples of the derivatives of pyrrole include3-methyl-pyrrole, 3-ethyl pyrrole, 3-ethenyl pyrrole, 3-methoxypyrrole,3-ethoxypyrrole, 3-phenylpyrrole, 3-phenoxypyrrole, 3-p-toluoylpyrrole,3-benzylpyrrole, 3-methoxymethylpyrrole, 3-p-fluorophenylpyrrole,3,4-dimethylpyrrole, 3,4-diethylpyrrole, 3,4-diethenylpyrrole,3,4-dimethoxypyrrole, 3,4-diethoxy-pyrrole, 3,4-diphenylpyrrole,3,4-diphenoxypyrrole, 3,4-di(p-toluoyl)pyrrole, 3,4-dibenzylpyrrole,3,4-dimethoxymethylpyrrole, and 3,4-di(p-fluorophenyl)-pyrrole.

In the following, “aniline or derivatives thereof” is simply referred toas “aniline”, and “at least one selected from the group consisting ofpolyaniline and derivatives thereof” is simply referred to as to“polyaniline” unless otherwise specified. In the same manner, “pyrroleor derivatives thereof” is simply referred to as “pyrrole”, and “atleast one selected from the group consisting of polypyrrole andderivatives thereof” is simply referred to as “polypyrrole” in thefollowing, unless otherwise specified. Therefore, if a polymer whichprovides conductive polymer is a derivative of aniline or pyrrole, thepolymer may be simply referred to as “a conductive polyaniline” or “aconductive polypyrrole”, respectively.

The conductive polyaniline can be obtained by electrochemicalpolymerization of aniline in the presence of a protonic acid or bychemical oxidation polymerization of aniline in the presence of aprotonic acid using an oxidizing agent in an appropriate solvent, aswell known, and preferably by chemical oxidation of aniline using anoxidizing agent. Water is usually used as the solvent, but a mixedsolvent such as a mixture of water soluble organic solvent and water, ora mixture of water and a nonpolar organic solvent is also used. Whenthese mixed solvents are used, a surfactant may be used if necessary.

Taking the chemical oxidation polymerization of aniline in water as anexample, the production of conductive polyaniline is explained in morespecifically. The chemical oxidation polymerization of aniline iscarried out using a chemical oxidizing agent in the presence of aprotonic acid in water. The chemical oxidizing agent may be either watersoluble or water insoluble.

Preferred oxidizing agents include, for example, ammoniumperoxodisulfate, hydrogen peroxide, potassium dichromate, potassiumpermanganate, sodium chlorate, cerium ammonium nitrate, sodium iodate,iron chloride, etc.

The amount of oxidizing agent used for oxidation of aniline hasinfluence on the yield of the conductive polyaniline obtained. Whenaniline is to be reacted quantitatively, it is preferred to use anoxidizing agent in an amount 2.5/n times in moles as much as the amountof the aniline used wherein n is the number of electrons required forone molecule of the oxidizing agent to be reduced. Therefore, whenammonium peroxodisulfate is used, n is 2, as seen from the followingequation:

(NH₄)₂S₂O₈+2e→2NH₄ ⁺+2SO₄ ²⁻

However, in some cases, the oxidizing agent may be used in an amount alittle less than 2.5/n times in moles as much as the amount of theaniline used, that is, in an amount of 30-80% of the amount 2.5/n timesin moles as much as the amount of the aniline used, so that the anilineis prevented from being brought into peroxidative status.

In the production of polyaniline, the protonic acid is used so that theaniline makes a salt in water and is made soluble in water, and thepolymerization system is kept strongly acidic at a pH of 1 or less, butalso the resulting polyaniline is doped therewith thereby to beconductive. Accordingly, the amount of the protonic acid used is notlimited so far as the above-mentioned purpose is accomplished, and it isusually 1.1 to 5 times in moles as much as the amount of the anilineused. However, a preferred amount is 1.1 to 2 times in moles as much asthe amount of the aniline used because when the amount of the protonicacid is too much, the expense for waste treatment after oxidationpolymerization of aniline increases to no purpose. Such being the case,the preferred protonic acid used is a strongly acidic one, and morespecifically, such a protonic acid that has an acid dissociationconstant pKa of less than 3.0.

As the protonic acid having such an acid dissociation constant pKa ofless than 3.0, there may be mentioned, for example, an inorganic acidsuch as sulfuric acid, hydrochloric acid, nitric acid, perchloric acid,tetrafluoroboric acid, hexafluorophosphoric acid, hydrofluoric acid, andhydroiodic acid, an aromatic sulfonic acid such as benzenesulfonic acidand p-toluenesulfonic acid, an aliphatic sulfonic acid (or an alkanesulfonic acid) such as methanesulfonic acid and ethanesulfonic acid.

A polymer having sulfonic acid groups in the molecule, that is, apolymer sulfonic acid, can be also used as a protonic acid. Such apolymer sulfonic acid includes, for example, polystyrenesulfonic acid,polyvinylsulfonic acid, polyallylsulfonic acid, poly(acrylic amidet-butylsulfonic acid), phenolsulfonic acid novolac resin,perfluorosulfonic acid represented by Nafion (registered trademark). Inthe invention, polyvinylsulfuric acid can also be used as a protonicacid.

In addition to the above-mentioned, a certain kind of phenols such aspicric acid, a certain kind of aromatic carboxylic acids such asm-nitrobenzoic acid, and a certain kind of aliphatic carboxylic acidssuch as dichloroacetic acid and malonic acid can be also used as aprotonic acid in the production of conductive polyaniline because theseacids have also an acid dissociation constant pKa of less than 3.0.

Among the various protonic acids mentioned above, tetrafluoroboric acidand hexafluorophosphoric acid are protonic acids which contain the sameanion species as an electrolyte or a salt of a base metal in anonaqueous electrolytic solution in a nonaqueous electrolyte secondarybattery. That is, in the case of lithium secondary battery, they areprotonic acids which contain the same anion species as an electrolyte ora lithium salt in a nonaqueous electrolytic solution in a lithiumsecondary battery. Thus, they are preferably used as a protonic acid inthe production of conductive polyaniline.

On the other hand, conductive polypyrrole is obtained by subjectingpyrrole to chemical oxidation polymerization by using a suitablechemical oxidizing agent in an aqueous solution of pyrrole containing anorganic sulfonate such as sodium alkylbenzenesulfonate, e.g., sodiumdodecylbenzenesulfonate and sodium anthraquinonesulfonate. Conductivepolypyrrole is also obtained as thin film on an anode by subjectingpyrrole to electrochemical oxidation polymerization using a stainlesssteel electrode in an aqueous solution of pyrrole containing a sodiumalkylbenzenesulfonate or an organic sulfonate.

In such a method for producing conductive polypyrrole as mentionedabove, the sodium alkylbenzene-sulfonate and organic sulfonate act as anelectrolyte, while alkylbenzene-sulfonic acid anions and organicsulfonic acid anions function as a dopant of polypyrrole formed toprovide polypyrrole with conductivity.

According to the invention, as set forth above, the conductive polymermay be a polymer doped with protonic acid anions, or may be a polymer ina dedoped state obtained by dedoping the above-mentioned polymer dopedwith protonic acid anions. If necessary, the polymer in dedoped statemay be further reduced.

As a method for dedoping a conductive polymer, there may be mentioned amethod in which, for example, a conductive polymer doped with a protonicacid is neutralized with an alkali. Also as a method for dedoping andthen reducing a conductive polymer doped with a protonic acid, there maybe mentioned a method in which, for example, a conductive polymer isdedoped by neutralization with an alkali, and the thus obtained dedopedpolymer is reduced with a reducing agent.

In order to neutralize a conductive polymer doped with a protonic acidby use of an alkali, the polymer is put in an aqueous solution of alkalisuch as sodium hydroxide solution, potassium hydroxide solution, orammonia water, and the resulting mixture is stirred at a roomtemperature, or at a temperature of 50-80° C. with heating, ifnecessary. When the mixture is treated with an alkali with heating inthis way, the dedoping reaction of conductive polymer is accelerated,and the conductive polymer is dedoped within a short period of time.

On the other hand, in order to reduce a polymer thus dedoped, thededoped polymer is put in a solution of reducing agent such as hydrazinemonohydrate, phenylhydrazine/alcohol, sodium dithionite, or sodiumsulfite, and the resulting mixture is stirred at a room temperature, orat a temperature of 50-80° C. with heating, if necessary.

The cathode sheet of nonaqueous electrolyte secondary battery of theinvention comprises a composite sheet which comprises a currentcollector and a layer comprising a solid cathode active material and aconductive auxiliary agent wherein the solid cathode active materialcomprises such a conductive polymer set forth above and at least oneselected from the group consisting of a polycarboxylic acid and a metasalt thereof. The layer comprising the cathode active material and theconductive auxiliary agent is porous. The polycarboxylic acid and ametal salt thereof were herein already set forth.

Taking a lithium secondary battery of which cathode comprises aconductive polyaniline as a conductive polymer as an example ofpreferred nonaqueous electrolyte secondary battery of the invention, thebehavior of polyaniline when the battery is charged and discharged isexplained with reference to the schemes 1 and 2 below.

The polyaniline obtained by dedoping a conductive polyaniline that isdoped with protonic acid anions by treating with an alkali and then byreducing the resulting product with a reducing agent comprisesimino-p-phenylene structural units shown as a formula (Ia). When asecondary battery of which cathode comprises a polyaniline whichcomprises such imino-p-phenylene structural units as stated above ischarged, the following is assumed to occur. At least some of thenitrogen atoms of the polyaniline which have unpaired electrons areone-electron oxidized, and as a result, cation radicals are produced,and the anions such as electrolyte anions (e.g., tetrafluoroborateanions) in an electrolytic solution or polycarboxylic acid anions (i.e.,polycarboxylate anions) in the electrode dope the polyaniline ascounterions for the cations thereby to produce a doped conductivepolyaniline (Ib) or (B).

On the other hand, when the lithium secondary battery is discharged, thecation radical sites in the above-mentioned conductive polyaniline (Ib)are reduced so that the conductive polyaniline returns to the originalpolyaniline (Ia) which has unshared electron pairs on the nitrogen atomsand is electrically neutral, as shown in a formula shown below,whereupon if the anions which are under coulomb interaction with thepolyaniline in the above-mentioned cation radical sites are electrolyteanions (for example, tetrafluoroborate anions), the electrolyte anionsmigrate toward the electrolyte from the neighborhood of the conductivepolymer.

However, if the anions which are under coulomb interaction with thepolyaniline in the above-mentioned cation radical sites arepolycarboxylic acid, for example, carboxylate anions of polyacrylic acid(IIIb), as shown below, the carboxylate anions cannot migrate toward theelectrolyte, unlikely the electrolyte anions (e.g., tetrafluoroborateanions), as they are polymeric anions, but they remain in theneighborhood of the polyaniline (IIa). Therefore, lithium cationsmigrate toward the neighborhood of the conductive polymer from theelectrolytic solution to make the above-mentioned carboxylate anionselectrically neutral, thereby to form salts (IIIa) as countercations forthe carboxylate anions.

According to the invention, the cathode sheet of the invention for usein the nonaqueous electrolyte secondary battery comprises a compositesheet which comprises a current collector and a layer provided on thecurrent collector, wherein the layer comprise a solid cathode activematerial comprising a conductive polymer and at least one selected fromthe group consisting of a polycarboxylic acid and a metal salt thereof,and a conductive auxiliary agent. The layer comprising the cathodeactive material and the conductive auxiliary agent is solid and porous.

The cathode sheet for use in the nonaqueous electrolyte secondarybattery is obtained as follows. For example, the at least one selectedfrom the group consisting of a polycarboxylic acid and a metal saltthereof is dissolved or dispersed in water; powder of a conductivepolymer and, if necessary, a conductive auxiliary agent such asconductive carbon black, is added to the resulting solution ordispersion, and are fully dispersed therein, to prepare a high viscositypaste having a solution viscosity of about 0.05-50 Pa·s; the paste iscoated on a current collector to form a layer of the paste; and thenwater is vaporized from the layer thereby to provide the cathode sheetin a form of a composite sheet which has on the current collector aneven layer comprising a cathode active material comprising a conductivepolymer and at least one selected from the group consisting of apolycarboxylic acid and a metal salt thereof, (and a conductiveauxiliary agent, if necessary).

It is preferred that the conductive auxiliary agent is a conductivematerial which is superior in conductivity and is effective to reduceelectrical resistance between the active materials of the electrodes,and further which does not change their properties depending uponelectric potential applied when the battery is charged and discharged.As the conductive auxiliary agent are usually used conductive carbonblack such as acetylene black and Ketjenblack, and fibrous carbonmaterial such as carbon fiber, carbon nanotube, and carbon nanofiber.

In the nonaqueous electrolyte secondary battery of the invention, thepolycarboxylic acid and a metal salt thereof have a function not only ofa binder in the preparation of the cathode but also of a dopant ofconductive polymer in the cathode, as set forth later, thereby tocontribute to improvement of performance of the nonaqueous electrolytesecondary battery of the invention, although the invention is notlimited to any theory.

In the nonaqueous electrolyte secondary battery of the invention, the atleast one selected from a polycarboxylic acid and a metal salt thereofis used usually in an amount of 1 to 100 parts by weight, preferably inan amount of 2 to 50 parts by weight, more preferably in an amount of 5to 30 parts by weight, per 100 parts by weight of a conductive polymer.When the amount of the at least one selected from a polycarboxylic acidand a metal salt thereof is too small in relation to the amount of theconductive polymer, a nonaqueous electrolyte secondary battery superiorin weight power density cannot be obtained. When the amount of the atleast one selected from a polycarboxylic acid and a metal salt thereofis too large in relation to the amount of the conductive polymer, anonaqueous electrolyte secondary battery superior in weight energydensity cannot be obtained because of increase in weight of membersexcept the cathode active material, when taking the whole weight of thebattery into consideration.

It is preferred that the porous layer of the cathode active material hasa porosity in a range of 35 to 80% so that the it has a high performanceas an electrode.

Further in the nonaqueous electrolyte secondary battery of theinvention, the electrolyte layer is, for example, a sheet of separatorwhich is impregnated with electrolytic solution, or a sheet formed ofsolid electrolyte. The sheet formed of solid electrolyte serves also asa separator.

As the electrolyte with which not only a separator but also electrodesare impregnated, there may be used, for example, a combination of a basemetal ion with an appropriate counter ion for the base metal ion, forexample, sulfonate ion, perchlorate ion, tetrafluoroborate ion,hexafluorophosphorate ion, hexafluoroarsenate ion,bis(trifluoromethanesulfonyl)imide ion,bis(pentafluoroethanesulfonyl)imide ion, and halogen ion.

According to the invention, the base metal refers to a metal which hasan ionization tendency larger than hydrogen, and is readily oxidized inthe air (when heated). An alkali metal such as lithium, sodium andpotassium, and an alkaline earth metal such as magnesium and calcium,and aluminum, zinc, and lead belong to the base metal.

Therefore, examples of the electrolyte mentioned above include LiCF₃SO₃,LiClO₄, LiBF₄, LiPF₆, LiAsF₆, LiN(SO₂CF₃)₂, LiN(SO₂C₂F₅)₂, LiCl,NaCF₃SO₃, NaClO₄, NaBF₄, NaPF₆, NaAsF₆, Ca(CF₃SO₃)₂, Ca(ClO₄)₂,Ca(BF₄)₂, Ca(PF₆)₂, Ca(AsF₆)₂, and so on.

The solvent for nonaqueous electrolyte includes, for example, at leastone nonaqueous solvent selected from the group consisting of acarbonate, a nitrile, an amide, and an ether, that is, an organicsolvent. Such an organic solvent includes, for example, ethylenecarbonate, propylene carbonate, butylene carbonate, dimethylcarbonate,diethylcarbonate, ethylmethyl-carbonate, acetonitrile, propionitrile,N,N′-dimethylacetamide, N-methyl-2-pyrrolidone, dimethoxyethane,diethoxyethane, and y-butyrolactone.

When a separator is used in the nonaqueous electrolyte secondary batteryof the invention, the separator is such that it is an insulative sheetwhich is capable of preventing electrical short circuit between acathode and an anode which are arranged to be opposite to each other andbetween which the separator is sandwiched, and which iselectrochemically stable, and has a large ion permeability, and inaddition, has a mechanical strength to a certain degree. Therefore,paper, nonwoven fabric, and a porous film formed of a resin such aspolypropylene, polyethylene, and polyimide is preferably used as aseparator.

In the nonaqueous electrolyte secondary battery of the invention, as ananode is used a base metal or a material into which base metal ions areinserted and from which base metal ions are extracted inoxidation/reduction reactions. The base metal includes, for example, analkali metal such as lithium or sodium metal, an alkaline earth metalsuch as magnesium or calcium metal, and the base metal ion includes, forexample, ions of the base metals stated above.

According to the invention, a preferred nonaqueous electrolyte secondarybattery is a lithium secondary battery. Accordingly, a preferred basemetal is lithium, and preferred base metal ions are lithium ions. As amaterial into which base metal ions are inserted and from which basemetal ions are extracted, a carbon material is preferably used, butsilicon and tin are also used.

The nonaqueous electrolyte secondary battery of the invention issuperior in weight power density and cycle characteristics like anelectric double layer capacitor, and in addition, it has a weight energydensity much higher than that of conventional electric double layercapacitors. Therefore, the nonaqueous electrolyte secondary battery ofthe invention can be said to be a capacitor-like secondary battery.

EXAMPLES

The invention will be explained in more detail with reference toexamples below, but the invention is not limited at all by theseexamples.

In the following, the porosity P of the layer of the cathode activematerial of the cathode sheet was calculated by the following equation:

P=((ST−V)/ST)×100

in which S is an area (cm²) of the cathode sheet; T is a thickness (cm)of the cathode sheet except the thickness of the current collector; andV is a volume (cm³) of the cathode sheet except the volume of thecurrent collector. The volume of the cathode sheet except the volume ofcurrent collector was calculated as follows. Using the proportion of theweight of the materials constituting the cathode sheet and the truedensity of each of the materials, an average density of the wholematerials of the cathode sheet was calculated, and then the total weightof the materials of the cathode sheet was divided by the averagedensity. The true densities of polyaniline, acetylene black (DenkaBlack) and polyacrylic acid are 1.2, 2.0 and 1.18, respectively.

Example 1 (Production of Conductive Polyaniline Powder HavingTetrafluoroborate Anions as a Dopant)

84.0 g (0.402 mol) of 42% by weight concentration aqueous solution oftetrafluoroboric acid (special grade; available from Wako Pure ChemicalIndustries, Ltd.) was put in 138 g of ion exchanged water in a 300 mLcapacity glass beaker. While stirring with a magnetic stirrer, 10.0 g(0.107 mol) of aniline was added to the resulting solution. At firstwhen the aniline was added to the aqueous solution of tetrafluoroboricacid, the aniline was found to be dispersed as oily droplets in theaqueous solution, and then within a few minutes the aniline wasdissolved in water to provide an even and transparent aqueous solutionof aniline. The aqueous solution of aniline obtained in this way wasthen cooled to a temperature of −4° C. or lower in a constant lowtemperature bath.

Then, 11.63 g (0.134 mol) of manganese dioxide powder (special grade;available from Wako Pure Chemical Industries, Ltd.), an oxidizing agent,was added to the aqueous solution of aniline in small portions while thetemperature of the mixture in the beaker was prevented from exceeding−1° C. When the oxidizing agent was added to the aqueous solution ofaniline in such a manner as mentioned above, the aqueous solution ofaniline immediately turned dark green. When stirring was continued for awhile, dark green solid began to be formed.

After the addition of oxidizing agent over a period of 80 minutes inthis way, the reaction mixture containing the resulting reaction productwas further stirred for 100 minutes while it was cooled. Then, theresulting solid was collected on No. 2 filter paper by suctionfiltration using a Buchner funnel and a suction bottle to obtain powder.The powder was stirred and washed in an aqueous solution oftetrafluoroboric acid having a concentration of about 2 mol/dm³ using amagnetic stirrer, and then in acetone several times, followed by vacuumfiltration. The obtained powder was vacuum dried at room temperature forten hours thereby 12.5 g of conductive polyaniline havingtetrafluoroborate anions as a dopant was obtained as bright greenpowder.

(Analysis of Conductive Polyaniline Powder)

FIG. 1 is an FT-IR spectrum of the conductive polyaniline powderobtained in this way. The adsorption peaks at 2918 cm⁻¹ are derived fromC—H stretching vibration of benzene ring; 1559 and 1479 cm⁻¹ are fromelongation stretching vibration of benzene ring; 1297 and 1242 cm⁻¹ arefrom C—N deformation vibration; and 1122 and 1084 cm⁻¹ are fromtetrafluoroboric acid doping polyaniline.

FIG. 2 is wide scan data of ESCA (photoelectron spectroscopy) spectrumof the above-mentioned conductive polyaniline powder, in which carbon,oxygen, nitrogen, boron and fluorine were observed, but sulfur andmanganese were not observed.

Based on the narrow scan data (not shown) of the ESCA spectrum of theabove-mentioned conductive polyaniline powder, the ratio of the elementsof the conductive polyaniline was obtained. Then, based on the ratio ofthe elements were obtained the ratio of 1/4 of the fluorine atoms to thenitrogen atoms in the conductive polyaniline as well as the ratio of theboron atoms to the nitrogen atoms in the conductive polyaniline. Namely,the doping ratios were obtained. As results, (F/4)/N was found to be0.33, and B/N was found to be 0.35.

As FIG. 3 shows a scanning electron micrograph (SEM) magnified 20000times, the conductive polyaniline powder was found to be agglomerates ofstick-like particles about 0.1 μm in diameter.

(Conductivity of Conductive Polyaniline Powder)

130 mg of the above-mentioned conductive polyaniline powder was groundwith an agate mortar. The resultant was subjected to vacuum pressmolding for ten minutes under a pressure of 300 MPa using a KBr tabletmolding machine for infrared spectrum measurement to provide a disk ofthe conductive polyaniline having a thickness of 720 μm. Theconductivity of the disk measured by four-terminal van der Pauw methodwas found to be 19.5 S/cm.

(Production of Cathode Sheet Comprising Conductive Polyaniline Powder)

0.1 g of polyacrylic acid (having a weight average molecular weight of1,000,000; available from Wako Pure Chemical Industries, Ltd.) was addedto 3.9 g of ion exchanged water, and left standing over night so that itswelled. Then, the polyacrylic acid was treated for one minute using asupersonic wave homogenizer to be dissolved in the ion exchanged waterto provide 4 g of even and viscous aqueous solution of polyacrylic acidhaving a concentration of 2.5% by weight.

0.8 g of the conductive polyaniline powder was mixed with 0.1 g ofconductive carbon black powder (Denka Black; available from Denki KagakuKogyo K.K.). The mixture was added to 4 g of the aqueous solution ofpolyacrylic acid and kneaded with a spatula, followed by treating themixture using a supersonic wave homogenizer to provide a fluid paste.The paste was then defoamed using a vacuum bottle and a rotary pump.

The defoamed paste was coated on a sheet of etched aluminum foil forelectric double layer capacitors (30CB; available from HohsenCorporation) at a coating rate of 10 mm/s with a micrometer-provideddoctor blade applicator using an automatic desk application devicemanufactured by Tester Sangyo K.K. After left standing for 45 minutes atroom temperature, the layer of the paste on the foil was dried on a hotplate at a temperature of 100° C. The resulting product was then pressedbetween a pair of stainless steel plates 15 cm square at a temperatureof 140° C. under a pressure of 1.49 MPa for five minutes using a vacuumpress (KVHC manufactured by Kitagawa Seiki K.K.) to provide a compositesheet.

The composite sheet thus obtained had a cathode active material whichcomprised the polyacrylic acid, the conductive polyaniline powder andthe conductive carbon black powder and which was found to have aporosity of 55%.

A disk was punched out from the composite sheet using a punching jighaving a punching blade 15.95 mm in diameter to provide a cathode sheet.Metal lithium (coin-shaped metal lithium; available from Honjo KinzokuK.K.) was used as an anode, while nonwoven fabric TF40-50 manufacturedby Hohsen Corporation and having a porosity of 68% was used as aseparator. These members were incorporated in a stainless steel HS cellfor experimental nonaqueous electrolyte secondary battery available fromHohsen Corporation K.K. The cathode sheet and the separator was vacuumdried at a temperature of 100° C. for five hours in a vacuum dryerbefore they were incorporated in the HS cell. The electrolyte was a 1mol/dm³ solution of lithium tetrafluoroborate (LIBF₄) in ethylenecarbonate/dimethyl carbonate (available from Kishida Kagaku K.K.). Alithium secondary battery was assembled in a glove box having a dewpoint of −100° C. in an atmosphere of super high purity argon gas.

The performance of the thus assembled lithium secondary battery wasevaluated in a constant current-constant voltage charge/constant currentdischarge mode using a current charge/discharge device (SD8 manufacturedby Hokuto Denko K.K.). Unless otherwise specified, the lithium secondarybattery was charged at a constant current with the final chargingvoltage of 3.8 V, and after the voltage reached 3.8 V, the lithiumsecondary battery was charged at a constant voltage of 3.8 V until thecurrent value reached 20% of the current value when being charged at theconstant current, followed by discharging at a constant current to thefinal discharging voltage of 2.0 V.

The results obtained when the lithium secondary battery was subjected tocharge/discharge cycle test at a charge/discharge current of 0.1 mA(except the period of the 29th to the 48th cycle in which thecharge/discharge current was 0.2 mA) were shown in FIG. 4 and FIG. 5.

FIG. 4 shows the relation between charge/discharge cycle number andweight capacity density, and FIG. 5 shows the relation between cyclenumber and weight energy density.

As clear from FIG. 4 and FIG. 5, both the weight capacity density andthe weight energy density of the lithium secondary battery of theinvention increased as the cycle number increased, and at the 62nd cyclethey reached a maximum, whereupon the weight capacity density was foundto be 84.6 Ah/kg and the weight energy density was found to be 277Wh/kg.

The rate characteristics of the lithium secondary battery were thenevaluated. The weight capacity density, weight energy density, andweight power density were measured as the charge/discharge rate waschanged from 0.5 C to 110 C. The results are shown in TABLE 1. The ratecharacteristics are those per the weight of cathode active material,that is, per the net weight of conductive polyaniline havingtetrafluoroborate anions as a dopant.

TABLE 1 Charge/ Cathode Weight Basis Discharge Weight Weight RateCapacity Density Energy Density Weight Power Density (C) (Ah/kg) (Wh/kg)(W/kg) 0.5 79.0 261.5 142 1.1 74.6 242.7 283 5 68.0 217.8 1394 11 65.0205.6 2752 27 60.3 185.1 6669 54 54.3 160.6 12803 110 45.6 129.1 24316

As well known, when a total capacity of X (mAh) of a battery isdischarged in an hour, the current value is X (mA), and the dischargerate is 1 C. The C is an initial of “capacity”. Accordingly, whencharge/discharge is carried out at a rate of 2 C, the current value is2× (mA), and the charge/discharge finishes in ½ hour, i.e., 30 minutes.On the other hand, when charge/discharge is carried out at a rate of 10C, the current value is 10× (mA), and the charge/discharge finishes in1/10 hour, i.e., 6 minutes.

Thus, a battery which can be charged and discharged at a large value ofC has a large battery output, and it is capable of being charged anddischarged rapidly. As clear from TABLE 1, the lithium secondary batteryassembled in Example 1 is a battery which has a very high outputperformance because it can be charged and discharged at a rate as highas 100 C or more.

FIG. 6 is a graph (charge/discharge curve) showing the relation betweenthe weight capacity density and voltage obtained when the lithiumsecondary battery was charged and discharged at various rates in a rangefrom 0.5 C to 110 C as shown in TABLE 1. Although the current value waschanged from 0.5 C to 110 C, that is, 220 times as much as 0.5 C, thecapacity was found to decrease from 79 Ah/kg to 45.6 Ah/kg, that is, toabout 60% what it was, showing that the lithium secondary batteryassembled in Example 1 is remarkably superior in output characteristics.A conventionally known lithium ion secondary battery would sufferremarkable decrease in capacity when the rate would reach about 3 C.

As stated above, the lithium secondary battery provided with a cathodesheet comprising a polyacrylic acid and a conductive polyanilineaccording to the invention has a high weight power density and superiorcycle characteristics like a capacitor and, besides, it has a weightenergy density 10 or more times higher than a capacitor.

FIG. 7 shows cycle characteristics obtained when the lithium secondarybattery was discharged at a rate as high as 8.3 C up to 6454 cycles. Thelithium secondary battery was charged at a constant current with thefinal charging voltage of 3.8 V, and after the voltage reached 3.8 V,the lithium secondary battery was charged at a constant voltage untilthe current value reached 20% of the current value when being charged atthe constant current, followed by discharging at a constant current tothe final discharging voltage of 3.0 V.

As a result, the lithium secondary battery was found to retain 90% ofthe initial weight energy density at the 1000th cycle, and 50% of theinitial weight energy density even at the 3000th cycle, showing that thelithium secondary battery of the invention has a remarkably superiorhigh cycle characteristics as compared with commonly known lithium ionbatteries.

Comparative Example 1

A lithium secondary battery was assembled in the same manner as inExample 1 except that polyacrylic acid was not used, but conductivepolyaniline powder obtained in Example 1 was used as it was. That is, ametal lithium anode and a separator were incorporated in a HS cellavailable from Hohsen Corporation K.K. After the separator was wettedwith the electrolytic solution, a predetermined amount of the conductivepolyaniline powder was adhered on the separator to assemble the battery.

TABLE 2 shows the relation between the charge/discharge rate and weightenergy density as well as the weight power density of the lithiumsecondary battery thus obtained. FIG. 8 also shows the relation betweencharge/discharge rates and weight energy density of the lithiumsecondary battery thus obtained together with the rate characteristicsof the lithium secondary battery assembled in Example 1.

TABLE 2 Charge/Discharge Rate Weight Energy Density Weight Power Density(C) (Wh/kg) (W/kg) 1.2 234.0 339 2.5 204.9 663 6.1 156.4 1570 12.3 116.12920 24.5 83.1 5422 36.8 65.9 7750 49.1 47.6 9835 61.3 29.5 11705 73.614.3 13299

The lithium secondary battery obtained in Comparative Example 1 wasfound to have a lower weight energy density over a whole range measuredas compared with the lithium secondary battery obtained in Example 1.

Example 2

Except the use of a hard carbon electrode which was prepared bypre-doping of hard carbon, that is, a low crystalline carbon materialavailable from Air Water K.K., with lithium, as an anode, in place ofmetal lithium, and otherwise in the same manner as in Example 1, abattery was assembled.

In a glove box, a lithium metal plate punched out so as to have adiameter of 15.5 mm was incorporated in the same HS cell as thatmentioned hereinbefore, and a separator made of nonwoven fabric waslayered on the lithium metal plate. 100 μL of an electrolytic solution,i.e., 1 mol/dm³ solution of lithium tetrafluoroborate (LIBF₄) inethylene carbonate/dimethyl carbonate was poured into the HS cell, andthen a hard carbon electrode punched out so as to have a diameter of15.95 mm was incorporated in the cell to provide a lithium secondarybattery.

The thus assembled lithium secondary battery was taken out of the glovebox, and a working electrode of a potentio/galvanostat (HZ-5000manufactured by Hokuto Denko K.K.) was connected to the carbonelectrode, and a counter electrode and reference electrode to thelithium metal electrode. The spontaneous potential was found to be about3 V.

While the working electrode was reduced at a constant current of 1 mA,the electric potential of the working electrode gradually decreased toreach 0.17 V. The constant current charging was continued for furtherone hour to pre-dope the hard carbon electrode with lithium. Then, whenthe battery was discharged at a constant current of 1 mA, the capacitywas found to be 195 mAh/g. After lithium pre-doping was carried outagain at a constant current of 1 mA, the HS cell was placed again in theglove box, and was broken up to take out the carbon electrode therefrom.

The lithium secondary battery was assembled by using the hard carbonelectrode pre-doped with lithium as an anode and a cathode which wasprepared in the same manner as Example 1. As shown in FIG. 9, thebattery reached a high weight energy density of 165 Wh/kg at 15th cycle,at a shorter cycle than in Example 1.

Example 3 (Production of Polyaniline Powder in a Reduced and DedopedState)

The production of conductive polyaniline was carried out at a scale 10times larger than in Example 1 to provide conductive polyaniline powderhaving tetrafluoroborate anions as a dopant as dark green powder.

The thus obtained conductive polyaniline powder in a dedoped state wasadded to a 2 mol/dm³ aqueous solution of sodium hydroxide, and themixture was stirred for 30 minutes to neutralize the conductivepolyaniline, thereby dedoping the tetrafluoroborate anions, the dopantof the polyaniline, from the polyaniline.

The thus dedoped polyaniline was washed with water until the filtratebecame neutral, stirred and washed in acetone, subjected to filtrationusing a Buchner funnel and a suction bottle thereby the dedopedpolyaniline powder was collected on No. 2 filter paper. The dedopedpolyaniline was vacuum dried for 10 hours at a room temperature toprovide dedoped polyaniline as brown powder.

The thus obtained polyaniline powder in a dedoped state was put in anaqueous methanol solution of phenylhydrazine, and stirred and reducedfor 30 minutes, whereupon the color of the polyaniline powder tuned grayfrom brown.

After the reduction treatment set forth above, the resulting polyanilinepowder was washed with methanol, and then with acetone, followed bycollecting by filtration, and vacuum drying at a room temperature, toprovide polyaniline powder in a reduced and dedoped state. FIG. 10 is anFT-IR spectrum of the polyaniline powder (KBr disk) in a reduced anddedoped state.

0.73 g of lithium hydroxide powder was added to 100 g of 4% by weightconcentration aqueous solution of polyacrylic acid to prepare an aqueoussolution of polyacrylic acid half lithium salt in which the half of thecarboxyl groups that the polyacrylic acid initially possessed were inthe form of lithium salts.

4.0 g of the polyaniline powder in a reduced and dedoped state was mixedwith 0.5 g of conductive carbon black powder (Denka Black; availablefrom Denki Kagaku Kogyo K.K.). The resulting mixture was added to 20.4 gof aqueous solution of the polyacrylic acid half lithium salt and wasdispersed therein using a supersonic wave homogenizer to prepare adispersion. The dispersion was further subjected to mild dispersiontreatment with a high shearing force using a dispersing machine, Filmix(registered trademark) Model 40-40 (manufactured by Primix Corporation)to obtain a fluid paste.

The paste was defoamed using a vacuum bottle and a rotary pump.

The paste was coated on a sheet of etched aluminum foil for electricdouble layer capacitors (30CB; available from Hohsen Corporation) at acoating rate of 10 mm/s with a micrometer-provided doctor bladeapplicator using an automatic desk application device manufactured byTester Sangyo K.K. After left standing for 45 minutes at roomtemperature, the layer of the paste on the foil was dried on a hot plateat a temperature of 100° C. The resulting product was then pressedbetween a pair of stainless steel plates 15 cm square at a temperatureof 140° C. under a pressure of 1.49 MPa for five minutes using a vacuumpress (KVHC manufactured by Kitagawa Seiki K.K.) to provide a compositesheet. The composite sheet thus obtained had a cathode active materialwhich was comprised of polyacrylic acid half lithium salt, conductivepolyaniline powder and conductive carbon black and which was found tohave a porosity of 71%.

A disk was punched out from the composite sheet using a punching jighaving a punching blade 15.95 mm in diameter to prepare a cathode sheet.This cathode sheet was incorporated in an HS cell to assemble a lithiumsecondary battery, and the performance of the battery was evaluated inthe same manner as Example 1. FIG. 11 shows the relation of the weightcapacity density vs. the charge/discharge cycle number, and FIG. 12shows the relation of the weight energy density vs. the charge/dischargecycle number.

Thus, as compared with the lithium secondary battery provided with acathode active material comprising conductive polyaniline powder whichhad tetrafluoroborate anions as a dopant and was in a doped state andpolyacrylic acid mentioned hereinbefore, the performance of which areshown in FIG. 4 and FIG. 5, the lithium secondary battery provided witha cathode active material comprising polyaniline powder in a reduced anddedoped state and polyacrylic acid half lithium salt was found to have aweight capacity density and a weight energy density each about twicehigher than the former battery in relation to the charge/discharge cyclenumber.

As a polyaniline in a reduced and dedoped polyaniline was used in thisexample, the weight capacity density and the weight energy density werecalculated by using only the weight of polyaniline which was in areduced and dedoped state, and had no dopant.

Examples 4-19

Production of polyaniline powder used in these examples 4-19 is setforth below, and ODIs (i.e., oxidation degree indexes) of thesepolyanilines are shown in TABLE 3.

The polyaniline powder used in these examples was produced as follows.The powder of conductive polyaniline which was doped withtetrafluoroborate anions and was obtained in Example 1 was added to a 2mol/dm³ solution of sodium hydroxide, the resulting was stirred with amagnetic stirrer for 30 minutes, washed with water and then withacetone, and the resulting neutralized product was vacuum dried at aroom temperature, thereby polyaniline in a dedoped state was obtained.

About 0.5 mg of the polyaniline in a dedoped state was dissolved in 200mL of N-methyl-2-pyrrolidone (NMP) to obtain a blue solution. Thesolution was put in a quartz cell having a light path length of 1 cm,and the electronic spectrum was measured from ultraviolet to visibleregion using a recording spectrophotometer. The electronic spectrumobtained was found to have two absorption maximums at wavelengths of 340nm and 640 nm. As shown in a formula below, the absorption at 340 nm isassigned to an amine structure (IVb) of the polyaniline while theabsorption at 640 nm is assigned to a quinonediimine structure (IVa) ofthe polyaniline.

Herein the invention, an ODI of polyaniline is defined to be a ratio ofthe absorbance A₆₄₀ of the absorption maximum at 640 nm assigned to thequinonediimine structure to the absorbance A₃₄₀ of the absorptionmaximum at 340 nm assigned to the amine structure, or a ratio ofA₆₄₀/A₃₄₀. Therefore, the ODI is an index to show a ratio of thequinonediimine structure of polyaniline, that is, a ratio of oxidizedstate of polyaniline.

The larger the value of ODI, the higher the oxidation degree ofpolyaniline, while the smaller the value of ODI, the lower the oxidationdegree of polyaniline, that is, the polyaniline is in a more reducedstate. When polyaniline has been completely reduced, and has noquinonediimine structure, but is composed only of the amine structure,the value of A₆₄₀ is zero, and hence the polyaniline has an ODI of zero.

The above-mentioned conductive polyaniline powder havingtetrafluoroborate anions as a dopant was treated with a 2 mol/dm³aqueous solution of sodium hydroxide, washed with water and then withacetone, and vacuum dried. The resulting polyaniline in a dedoped statewas found to have an ODI of 0.87.

A polyacrylic acid having a weight average molecular weight of 1,000,000and a polyacrylic acid having a weight average molecular weight of25,000 were respectively dissolved in water or isopropanol (IPA) toprepare solutions of polyacrylic acid each having a concentration shownin TABLE 3. Then, sodium hydroxide was added to and dissolved in each ofthe solutions in an amount shown in TABLE 4 to prepare binder solutions.The solutions are hereinafter referred to as polyacrylic acid (lithiumsalt) solutions.

The polyaniline powder which was obtained in such a manner as mentionedhereinbefore and was in a reduced and dedoped state was mixed with theconductive carbon black (Denka Black; available from Denki Kagaku KogyoK.K.) each in an amount shown in TABLE 3, and the resulting mixture wasadded to the polyacrylic acid (lithium salt) solution, followed bysubjecting to dispersion treatment using a supersonic wave homogenizer.When the resulting mixture has a high viscosity, it was diluted with adiluent in an amount as shown in TABLE 4 so that it had a viscositysuitable for the following treatment using a dispersing machine, Filmix(registered trademark). When it was diluted, the solid concentration ofthe mixture is shown as a paste concentration in TABLE 4. The mixturewas then further subjected to mild dispersion treatment with a highshearing force using a dispersing machine, Filmix (registered trademark)Model 40-40 (manufactured by Primix Corporation.) to obtain a fluidpaste. The paste was defoamed using a vacuum bottle and a rotary pump.

The amount and the ODI of the polyaniline powder, the mole ratio ofpolyacrylic acid (lithium salt)/polyaniline, the amount of theconductive auxiliary agent, the amount and the concentration ofpolyacrylic acid (lithium salt) in the polyacrylic acid (lithium salt)solution, the amount of lithium hydroxide used to lithiate thepolyacrylic acid and lithiation ratio are shown in TABLE 3 and TABLE 4.The total weight of the paste thus obtained, the solid content, theconcentration of paste, the solid content of polyaniline, the solidcontent of conductive auxiliary agent, the solid content of polyacrylicacid, and the coating thicknesses (wet) of the paste on a collector areshown in TABLE 4 and TABLE 5.

In example 14-19, the above-mentioned paste was coated in a thickness(wet) shown in TABLE 4 on a sheet of etched aluminum foil for electricdouble layer capacitors (30CB; available from Hohsen Corporation) at acoating rate of 10 mm/s with a micrometer-provided doctor bladeapplicator using an automatic desk application device manufactured byTester Sangyo K.K. After left standing for 45 minutes at roomtemperature, the layer of the paste on the foil was dried on a hot plateat a temperature of 100° C. to obtain a composite sheet comprising thecollector and a cathode active material formed thereon and having aporosity shown in TABLE 5.

In example 4-13, the paste was coated in a thickness (wet) shown inTABLE 5 on a sheet of etched aluminum foil for electric double layercapacitors (30CB; available from Hohsen Corporation) at a coating rateof 10 mm/s with a micrometer-provided doctor blade applicator using anautomatic desk application device manufactured by Tester Sangyo K.K.After left standing for 45 minutes at room temperature, the layer of thepaste was dried on a hot plate at a temperature of 100° C. The resultingproduct was then pressed between a pair of stainless steel plates 15 cmsquare at a temperature of 140° C. under a pressure of 1.49 MPa for fiveminutes using a vacuum press (KVHC manufactured by Kitagawa Seiki K.K.)to provide a composite sheet comprising the cathode active materialformed on the collector and having a porosity shown in TABLE 5.

Then, the composite sheet thus obtained was cut to a size of 35 mm×27mm, and a part of the layer of active material was removed so that thelayer of the active material of the composite sheet had an area of 27mm×27 mm. A tab electrode was attached to the portion at which the layerof the active material was removed to prepare a cathode sheet. Usingthis cathode sheet, a laminate battery was assembled, in which an anodewas so made that it had an area of 29 mm×29 mm, slightly larger than thecathode sheet.

The weight of each of the components of the cathode active material percathode sheet, that is, the weight of each of the polyaniline,conductive auxiliary agent and polyacrylic acid, is shown in TABLE 5.

A piece of aluminum foil 50 μm thick was connected to a cathodecollector (aluminum foil) with a spot welder to make a tab electrode totake out current at the cathode.

The cathode to which a tab electrode had been attached, a stainlesssteel mesh electrode as an anode, and a separator were vacuum dried at atemperature of 80° C., and then a piece of metal lithium was pressedagainst the stainless steel mesh electrode to stick the lithium metaltherein to prepare an anode in a glove box having a dew point of −100°C. A separator shown in TABLE 5 was interposed between the cathode andthe anode, and the resulting assembly was inserted into a laminate cellthrough a mouth formed by their three verges heat sealed. The positionof the separator was adjusted so that the cathode and anode were inopposite position to each other correctly and did not short. Further, asealing agent was applied to the tab electrode of each of the cathodeand the anode, and the portions at which the tab electrodes wereattached were so heat sealed as to leave an opening for an electrolyticsolution.

A predetermined amount of electrolytic solution was poured into thelaminate cell through the opening using a micropipette, and then theopening was heat sealed and closed to obtain a laminate cell. The amountof electrolytic solution used is shown in TABLE 5.

The battery performance of the laminate cell thus obtained wasevaluated. TABLE 6 shows the conditions for evaluating the batteryperformance together with the initial charging capacity, the initialdischarging capacity, the initial weight capacity density and theinitial weight energy density at the first cycle, as well as thedischarging capacity, the weight capacity density and the weight energydensity at the fifth cycle.

TABLE 3 Materials Used For Production Of Cathode Sheet ConductivePolyacrylic Auxiliary Acid/Polyaniline Polyacrylic Acid PolyanilineAgent Mole Ratio Average Molecular Polyacrylic Acid Solution Examples gODI g % Weight wt % g Solvent 4 4 0.25 0.5 27.8 1,000,000 4.4 20.0 Water5 6 0.21 0.75 27.8 1,000,000 4.4 30.0 ″ 6 6 0.21 0.75 27.8 1,000,000 4.430.0 ″ 7 4 0.04 0.5 27.8 1,000,000 4.4 20.0 ″ 8 4 0.11 0.5 28.4 250004.5 20.0 ″ 9 4 0.11 0.5 28.5 25000 4.4 20.5 ″ 10 4 0.22 0.5 50.41,000,000 7.6 21.0 ″ 11 6 0.024 0.75 28.7 1,000,000 4.4 31.0 ″ 12 4 0.210.5 27.8 1,000,000 4.4 20.0 ″ 13 4 0.21 0.5 27.7 1,000,000 7.6 11.5 IPA14 4 0.06 0.5 28.4 1,000,000 4.4 20.4 Water 15 4 0.06 0.75 28.41,000,000 4.4 20.4 ″ 16 4 0.06 1.0 28.4 1,000,000 4.4 20.4 ″ 17 4 0.060.5 28.4 1,000,000 4.4 20.4 ″ 18 4 0.06 0.5 28.4 1,000,000 4.4 20.4 ″ 194 0.02 0.5 28.3 1,000,000 4.2 21.3 ″

TABLE 4 Paste Used For Production Of Active Material Layer Of CathodeSheet Materials Used For Production Of Active Conductive Material LayerOf Cathode Sheet Polyaniline Auxiliary Polyacrylic Lithium HydroxideSolid Total Paste Solid Agent Solid Acid Solid Weight Lithiation RatioContent Weight Concentration Content Content Content Examples g %Diluent g g wt % wt % wt % wt % 4 0.00 0 Water 5.38 24.50 22.0 74 9 16 50.22 50 ″ 8.29 36.97 22.4 72 9 19 6 0.22 50 ″ 8.29 36.97 22.4 72 9 19 70.14 50 ″ 5.52 26.14 21.1 72 9 19 8 0.00 0 ″ 5.40 24.50 22.0 74 9 17 90.00 0 ″ 5.40 24.99 21.6 74 9 17 10 0.00 0 ″ 6.10 27.50 22.2 66 8 26 110.23 50 ″ 8.34 39.98 20.9 72 9 19 12 0.00 0 ″ 5.38 24.50 22.0 74 9 16 130.00 0 IPA 5.37 20.01 26.9 74 9 16 14 0.15 50 Water 5.55 29.05 19.1 72 919 15 0.15 50 ″ 5.80 30.30 19.1 69 13 18 16 0.15 50 ″ 6.05 30.55 19.8 6617 17 17 0.30 100 ″ 5.70 32.20 17.7 70 9 21 18 0.30 100 ″ 5.70 38.2014.9 70 9 21 19 0.15 50 ″ 5.54 28.95 19.1 72 9 19

TABLE 5 Active Material Layer Of Cathode Sheet Coating Lithium SecondaryBattery Thickness Weight Of Constituents of Active Material LayerLithium Ratio Amount of Of Paste Per Cathode Sheet (mg) Of PolyacrylicSeparator Electrolytic (wet) Conductive Polyacrylic Acid Void RatioConstituents × Number Solution Examples μm Polyaniline Auxiliary AgentAcid mol % % of Sheets μL 4 360 34.8 4.4 7.7 0 49.5 Nonwoven Fabric × 2164 5 360 37.9 4.7 8.3 50 52.8 *⁾ CG2400 × 1 164 6 360 36.2 4.5 8.0 5064.3 Nonwoven Fabric × 2 164 7 360 70.4 8.8 15.5 50 55.1 CG2400 × 1 1648 360 18.1 2.3 4.1 0 59.7 Nonwoven Fabric × 2 164 9 360 36.2 4.5 8.2 070.0 Nonwoven Fabric × 2 164 10 720 45.9 5.7 18.3 0 49.4 Nonwoven Fabric× 2 164 11 360 34.4 4.3 7.8 50 63.6 Nonwoven Fabric × 2 164 12 360 27.53.4 6.1 0 73.2 Nonwoven Fabric × 2 164 13 360 37.2 4.7 8.1 0 68.6Nonwoven Fabric × 2 164 14 360 26.5 3.3 5.9 50 73.2 Nonwoven Fabric × 2246 15 360 26.2 4.9 5.9 50 71.4 Nonwoven Fabric × 2 246 16 360 24.3 6.15.5 50 75.0 Nonwoven Fabric × 2 246 17 360 28.3 3.5 6.4 100 68.5Nonwoven Fabric × 2 246 18 360 21.1 2.6 4.7 100 76.8 Nonwoven Fabric × 2246 19 360 25.4 3.2 5.7 50 71.3 Nonwoven Fabric × 3 328 *⁾ Separatormade of polypropylene available from Celguard (having a porosity of 41%)

TABLE 6 Battery Performance Conditions For Evaluation Of BatteryPerformance At The Fifth Battery Performance Battery Performance At TheFirst Cycle Cycle Initial Initial Weight Weight Weight Charge/DischargeInitial Charge Discharge Capacity Initial Weight Discharge CapacityEnergy Current Value 1 C Capacity Capacity Density Energy DensityCapacity Density Density Examples C mA mA mAh mAh Ah/kg Wh/kg mAh Ah/kgWh/kg 4 0.05 0.26 5.12 4.0 4.5 130 414 4.4 126 404 5 0.05 0.28 5.57 3.43.7 96 301 4.1 108 345 6 0.05 0.27 5.32 4.3 6.2 171 530 6.3 174 548 70.05 0.52 10.35 0.2 4.7 67 200 4.8 68 205 8 0.03 0.09 2.66 2.2 3.0 164528 4.4 246 757 9 0.03 0.18 5.32 4.2 7.2 200 636 6.8 188 582 10 0.030.23 6.75 5.2 6.6 143 416 6.6 144 460 11 0.05 0.25 5.06 4.2 6.3 185 5556.4 186 592 12 0.03 0.14 4.04 3.4 4.4 160 506 4.6 168 540 13 0.03 0.195.47 4.1 3.8 103 322 3.4 91 293 14 0.05 0.20 3.90 3.5 3.9 146 464 3.7139 448 15 0.05 0.19 3.85 3.6 4.1 155 495 4.2 161 523 16 0.05 0.18 3.573.7 4.3 177 567 4.7 192 627 17 0.05 0.21 4.16 4.4 4.5 159 511 4.7 167544 18 0.05 0.16 3.10 3.2 3.3 155 496 3.6 169 548 19 0.05 0.19 3.74 3.24.3 167 539 4.1 160 518

Example 20

11.47 g of toluidine was used in place of 10.0 g of aniline, andotherwise in the same manner as in Example 1, conductivepoly(o-toluidine) which had tetrafluoroborate anions a dopant and was inan oxidized and doped state was obtained as powder. Using thisconductive poly(o-toluidine), a lithium secondary battery was assembledin the same manner as in Example 1, and the battery performance wasevaluated.

FIG. 13 shows an FT-IR spectrum of conductive poly(o-toluidine) whichhad tetrafluoroborate anions as a dopant and was in an oxidized anddoped state (KBr disk). FIG. 14 shows the relation of the weightcapacity density vs. charge/discharge cycle number. FIG. 15 shows therelation of the weight energy density vs. charge/discharge cycle number.In the measurement of the performance of the lithium secondary battery,the battery was discharged at a constant current of 0.1 mA from the 1stto the 20th cycle, and then discharged at a constant current of 0.5 mAfrom the 41st to the 60th cycle.

The relations of each of the weight capacity density and the weightenergy density vs. charge/discharge cycle number obtained when thebattery was thereafter discharged at a constant current of 0.1 mA fromthe 1st to the 12th cycle are shown in FIG. 16 and FIG. 17. The lithiumsecondary battery showed stable cycle characteristics.

Example 21

(Production of Conductive Polypyrrole Powder Havinganthraquinone-2-sulfonate Anions as a Dopant)

25 g of pyrrole (0.373 mol) was dissolved in 430 g of ion exchangedwater with stirring to prepare a 5.5% by weight aqueous solution, towhich was dissolved 30.5 g (0.093 mol) of sodiumanthraquinone-2-sulfonate monohydrate.

Then, 243 g of 35% by weight aqueous solution of ammoniumperoxodisulfate was added dropwise in portions to the solution ofpyrrole containing the sodium anthraquinone-2-sulfonate in two hours.After the reaction, the resulting reaction mixture was vacuum filtratedusing a Buchner funnel and a suction bottle to provide black powder. Thepowder was washed with water, and then with acetone, followed by vacuumdrying in a desiccator at a room temperature for ten hours, to provide25.5 g of conductive polypyrrole having anthraquinone-2-sulfonate anionsas a dopant as black powder. FIG. 18 is an FT-IR spectrum of theconductive polypyrrole powder in a doped state.

In the FT-IR spectrum, 3455 cm⁻¹ is assigned to N—H stretchingvibration; 1670 cm⁻¹ is assigned to stretching vibration of carbonylgroups of anthraquinone-2-sulfonate anions; 1542 cm⁻¹ is assigned tostretching vibration of C—C double bonds of pyrrole rings; 1453 cm⁻¹ isassigned to C—H bending vibration of pyrrole rings; 1290 cm⁻¹ isassigned to C—N stretching vibration of pyrrole rings; and 1164 cm⁻¹ isassigned to stretching vibration of S—O double bonds ofanthraquinone-2-sulfonate anions.

The S/N atomic ratio in the above-mentioned conductive polypyrrolepowder was found to be 0.15 as measured by ESCA, showing that the dopingrate by the anthraquinone-2-sulfonate anions was found to be 0.15.

(Conductivity of conductive polypyrrole powder) 130 mg of theabove-mentioned conductive polypyrrole powder was press molded toprovide a disk 13 mm in diameter and 720 μm in thickness. The disk wassubjected to measurement of conductivity by van der Pauw method. Theconductivity was found to be 10 S/cm.

(Production of a Cathode Sheet Comprising Conductive Polypyrrole Powder)

3 g of the conductive polypyrrole powder was mixed with 0.44 g ofconductive carbon black (Denka Black; available from Denki Kagaku KogyoK.K.). The mixture was added to 24 g of 4.5% by weight aqueous solutionof polyacrylic acid half lithium salt. The resulting mixture was kneadedwith a spatula, and was then subjected to dispersion treatment using asupersonic wave homogenizer to provide a dispersion. 5 g of ionexchanged water was added to the dispersion, and the resultant wassubjected to dispersion treatment using a supersonic wave homogenizer toprovide a paste. The paste was then further subjected to mild dispersiontreatment at a linear velocity of 20 m/s for 30 seconds with a highshearing force using a dispersing machine, Filmix (registered trademark)Model 40-40 (manufactured by Primix Corporation) to obtain a viscosepaste.

Then in the same manner as in Example 1, the paste was coated on a sheetof etched aluminum foil for electric double layer capacitors (30CB;available from Hohsen Corporation) at a coating rate of 10 mm/s with amicrometer-provided doctor blade applicator using an automatic deskapplication device manufactured by Tester Sangyo K.K. After air dryingfor 45 minutes at room temperature, the layer of the paste was dried ona hot plate at a temperature of 100° C. to provide a composite sheet.

The composite sheet thus obtained had a cathode active material whichcomprised the conductive polypyrrole powder, polyacrylic acid, and theconductive carbon black powder and which was found to have a porosity of65.9%.

A disk was punched out from the composite sheet using a punching jighaving a punching blade 15.95 mm in diameter to prepare a cathode sheet.Metal lithium (coin-shaped metal lithium; available from Honjo KinzokuK.K.) was used as an anode, while nonwoven fabric TF40-50 manufacturedby Hohsen Corporation and having a porosity of 68% was used as aseparator. These members were incorporated in a stainless steel HS cellfor experimental nonaqueous electrolyte secondary battery manufacturedby Hohsen Corporation. The cathode sheet and the separator was vacuumdried at a temperature of 100° C. for five hours in a vacuum dryerbefore they were incorporated in the HS cell. The electrolytic solutionused was a 1 mol/dm³ solution of lithium tetrafluoroborate (LIBF₄) inethylene carbonate/dimethyl carbonate (available from Kishida KagakuK.K.). A lithium secondary battery was assembled in an atmosphere ofsuper high purity argon gas in a glove box having a dew point of −100°C.

The performance of the thus assembled lithium secondary battery wasevaluated in a constant current-constant voltage charge/constant currentdischarge mode using a current charge/discharge device (SD8 manufacturedby Hokuto Denko K.K.). That is, unless otherwise specified, the lithiumsecondary battery was charged at a constant current with the finalcharging voltage of 3.8 V, and after the voltage reached 3.8 V, thelithium secondary battery was charged at a constant voltage until thecurrent value reached 20% of the current value while the lithiumsecondary battery was charged at a constant current, followed bydischarging at a constant current to the final discharging voltage of2.0 V.

The results obtained when the lithium secondary battery was subjected tocharge/discharge test at a charge/discharge rate of 0.5 C are shown asthe curves of PALiDR=0.31(1) and (2) in FIG. 19. Herein the drawing,PALiDR=0.31 means that in the preparation of cathode active material,the polyacrylic acid half lithium salt was used in an amount (in moles)0.31 times as much as the amount (in moles) of the nitrogen atoms of thepolypyrrole, that is, the DR (doping rate) was 0.31.

A lithium secondary battery of which cathode comprises conductivepolypyrrole needs to be charged/discharged to some degree until apredetermined capacity is obtained, that is, the battery needs initialactivation. FIG. 19 shows the relation between the charge/dischargecycle number and the weight capacity density during the process ofinitial activation of the lithium secondary battery of which cathodecomprises conductive polypyrrole.

The doping rate of the polypyrrole have been said to be usually 0.25 sofar, and when the polypyrrole has the doping rate, the theoreticalweight capacity density per weight of polypyrrole is 103 mAh/g. However,as the performance of lithium secondary battery comprising conductivepolypyrrole and polyacrylic acid is shown as the curve of PALiDR=0.31 inFIG. 19, the capacity density per weight of polypyrrole at the cathodeis as high as 120-130 mAh/g, which exceeds the value of 103 mAh/g. Thisvalue is 0.3 when converted to a doping rate of polypyrrole, and ishigher than 0.25, a value which has been conventionally accepted dopingrate.

The results of charge/discharge cycle tests of lithium secondary batterycomprising a cathode sheet prepared by using a binder composed of amixture of styrene-butadiene copolymer (SBR)/carboxymethylcellulose(CMC) in place of lithium polyacrylate are also shown as the curves ofSBR/CMC (1) and (2) in FIG. 19.

In turn, PPy-PALi in FIG. 20 is a plotted curve of weight capacitydensity obtained when the charge/discharge current value of lithiumsecondary battery provided with a cathode comprising conductivepolypyrrole and polyacrylic acid was increased from 0.05 C to 100 C,that is, the rate characteristics. In the same manner, the curvePPy-SBR/CM shows the rate characteristics of lithium secondary batteryprovided with a cathode comprising conductive polypyrrole and SBR/CMC.Both the lithium secondary batteries retain a high capacity density at acharge/discharge rate of 10 C or higher, thus being superior in rapidcharge/discharge performance.

FIG. 21 shows cycle characteristics of lithium secondary battery(PPy-PALi0.5) provided with a cathode comprising conductive polypyrroleand polyacrylic acid, and of a lithium secondary battery (PPy-SBR/CMC)provided with a cathode comprising conductive polypyrrole and SBR/CMC ata charge/discharge rate as high as 10 C. Both the batteries were foundto maintain a capacity retention as high as 85-90% even at a relativelymany charge/discharge cycles of 400.

Comparative Example 2

A lithium secondary battery was assembled using neither polyacrylic acidnor SBR/CMC, but using conductive polypyrrole powder obtained in Example21 as it was as a binder, and otherwise in the same manner as in Example21. Namely, a metal lithium anode and a separator were incorporated inan HS cell manufactured by Hohsen Corporation, and the separator waswetted with electrolytic solution, and then a predetermined amount ofconductive polypyrrole powder was adhered onto the separator, thereby abattery was assembled.

The weight density data and the charge/discharge rate characteristics inthe initial activation process of lithium secondary battery thusobtained are shown as two curves of “no binder (1)” and “no binder (2)”in FIG. 19, and as a curve of “PPY-no binder” in FIG. 20. When thecathode contained neither polyacrylic acid nor SBR/CMC as a binder, theweight capacity density of the resulting lithium secondary battery waslower than 103 mAh/g or the theoretical capacity density, as shown by“no binder” in FIG. 19. That is, it is clear that the resulting lithiumsecondary battery had a capacity smaller than the lithium secondarybattery obtained by using polyacrylic acid or SBR/CMC as a binderaccording to the present invention.

It is also cleat that the above-mentioned lithium secondary battery isinferior in rate characteristics as compared with the lithium secondarybattery obtained by using polyacrylic acid as a binder according to theinvention, as shown by the results of “PPY-no binder” in FIG. 20.

Example 21 (Production of Cathode Sheet Comprising ConductivePolyaniline Powder)

4.00 g of the conductive polyaniline powder obtained in Example 1 wasmixed with 0.45 g of conductive carbon black (Denka Black; availablefrom Denki Kagaku Kogyo K.K.). The mixture was mixed with 1.43 g ofaqueous solution of polymaleic acid (Nonpole PMA-50W containingpolymaleic acid in an amount of 50% by weight; available from NichiyuK.K.) and 16.0 g of distilled water, and the resulting mixture waskneaded with a spatula. The mixture was then subjected to dispersiontreatment using a supersonic wave homogenizer to provide a dispersion,and then subjected to high rate dispersion treatment at a linearvelocity of 20 m/s for 30 seconds using a dispersing machine, Filmix(registered trademark) Model 40-40 (manufactured by Primix Corporation)to obtain a fluid paste. The paste was defoamed for three minutes.

Then, the defoamed paste was coated on a sheet of etched aluminum foilfor electric double layer capacitors (30CB; available from HohsenCorporation) at a coating rate of 10 mm/s with a micrometer-provideddoctor blade applicator using an automatic desk application devicemanufactured by Tester Sangyo K.K. After air drying for 45 minutes atroom temperature, the layer of the paste was dried on a hot plate at atemperature of 100° C. to provide a composite sheet.

The composite sheet thus obtained had a layer of the cathode activematerial which comprised the conductive polyaniline powder, theconductive carbon black powder, and polyacrylic acid, and was found tohave a thickness of 44 μm and a porosity of 56%.

A laminate cell was assembled in the same manner as in Examples 4 to 19.The materials used for preparation of cathode sheet, the composition ofpaste, the ratios of materials in the layer of active material, theconditions for assembling the laminate cell, and the obtained batteryperformance data are shown in TABLE 7 to TABLE 10. The laminate cellassembled using polymaleic acid as a binder was found to have a highcapacity density and energy density in the same manner as the case wherea polyacrylic acid binder was used.

TABLE 7 Materials Used For Production Of Active Material Layer OfCathode Sheet Conductive Polymaleic Auxiliary Acid/PolyanilinePolymaleic Acid Polyaniline Agent Mole Ratio Average Molecular SolutionOf Polymaleic Acid Examples g ODI g % Weight wt % g Solvent 21 4 0.2 0.527.8 — 50 1.4 Water

TABLE 8 Paste Used For Production Of Active Material Layer Of CathodeSheet Materials Used For Production Of Active Conductive Material LayerOf Cathode Sheet Polyaniline Auxiliary Polyacrylic Lithium HydroxideSolid Total Paste Solid Agent Solid Acid Solid Weight Lithiation RatioContent Weight Concentration Content Content Content Examples g %Diluent g g wt % wt % wt % wt % 21 — — Water 5.2 22.1 24.0 77 9 14

TABLE 9 Active Material Layer Of Cathode Sheet Coating Weight OfConsitituents Of Active Material Layer Void Ratio Lithium SecondaryBattery Thickness Per Cathode Sheet (mg) Lithiation Ratio Of ActiveSeparator Amount Of Of Paste Conductive Of Polyacrylic MaterialConstituents × Electrolytic (wet) Auxiliary Acid Layer Number OfSolution Examples μm Polyaniline Agent Polymaleic Acid mol % % Sheets μL21 360 7.4 0.9 1.2 0 55.7 Nonwoven 230 Fabric × 3

TABLE 10 Battery Performance Conditions For Evaluation BatteryPerformance At The Fifth Of Battery Performance Battery Performance AtThe First Cycle Cycle Initial Initial Weight Initial Weight WeightWeight Charge/Discharge Initial Charge Discharge Capacity EnergyDischarge Capacity Energy Current Value 1 C Capacity Capacity DensityDensity Capacity Density Density Examples C mA mA mAh mAh Ah/kg Wh/kgmAh Ah/kg Wh/kg 21 0.05 0.101 2.03 1.9 2.0 145 458 2.0 147 472

Example 22 (Production of a Cathode Sheet Comprising Polyaniline in aReduced and Dedoped State)

4.4 g of polyacrylic acid (having a weight average molecular weight of1000000; available from Wako Pure Chemical Industries, Ltd.) was addedto 95.6 g of ion exchanged water, and left standing over night so thatit swelled. Then, the resulting mixture was treated for one minute witha supersonic wave homogenizer so that it was dissolved in the ionexchanged water to provide 100 g of uniform and viscous aqueous solutionof polyacrylic acid having a concentration of 4.4% by weight.

0.73 g of lithium hydroxide powder was added to 100 g of the aqueoussolution of polyacrylic acid to lithiate the half of the amount of thecarboxylic groups that the polyacrylic acid possessed to prepare anaqueous solution of polyacrylic acid half lithium salt.

4.0 g of the conductive polyaniline powder which was obtained in Example3 and was in a reduced and dedoped state was mixed with 0.5 g ofconductive carbon black powder (Denka Black; available from Denki KagakuKogyo K.K.). The mixture was added to 20.4 g of the aqueous solution ofpolyacrylic acid half lithium salt and kneaded together with a spatula.

The resulting mixture was subjected to dispersion treatment using asupersonic wave homogenizer to provide a dispersion, and then subjectedto mild dispersion treatment with a high shearing force using adispersing machine, Filmix (registered trademark) Model 40-40(manufactured by Primix Corporation) to obtain a fluid paste. The pastewas defoamed using a suction bottle and a rotary pump.

The defoamed paste was coated in a thickness of 360 μm on a sheet ofetched aluminum foil for electric double layer capacitors (30CB;available from Hohsen Corporation) at a coating rate of 10 mm/s with amicrometer-provided doctor blade applicator using an automatic deskapplication device manufactured by Tester Sangyo K.K.

The resulting was air dried for 45 minutes at room temperature, and wasthen dried on a hot plate at a temperature of 100° C., followed bypressing between a pair of stainless steel plates 15 cm square at atemperature of 140° C. under a pressure of 1.5 MPa for five minutesusing a vacuum press (KVHC manufactured by Kitagawa Seiki K.K.) toprovide a composite sheet. This composite sheet was used as a cathodesheet as set forth in the following.

(Production of Laminate Cell)

Two sheets of porous membrane formed of polypropylene obtained fromHohsen Corporation (Celgard (registered trademark) 2400 produced byCelgard; having a thickness of 25 μm, a porosity of 38%, an airpermeability of 620 s/100 cm³) were put together to prepare a separator.The anode was metal lithium foil 50 μm thick obtained from Honjo KinzokuK.K.

Then, the anode, cathode and separator were assembled to provide astack. More particularly, the separator was interposed between thecathode and the anode to prepare the stack. The stack was put in analuminum laminated package, and vacuum dried at 80° C. for two hours.

LiPF₆ was dissolved in a concentration of 1 mol/dm³ in a solventcomposed of ethylene carbonate and dimethyl carbonate in a volume ratioof 1:1 to prepare an electrolytic solution. The electrolytic solutionwas poured into the laminated package, and then the package was sealedto provide a nonaqueous electrolyte secondary battery of the invention.The electrolytic solution was poured into the package in an atmosphereof super high purity argon gas in a glove box having a dew point of −90°C.

The performance of the thus assembled nonaqueous electrolyte secondarybattery was evaluated in a constant temperature bath at a temperature of25° C. The performance was evaluated in a constant current-constantvoltage charge/constant current discharge mode using a currentcharge/discharge device (SD8 manufactured by Hokuto Denko K.K.). Thebattery was charged at 0.174 mA with the final charging voltage of 3.8V, and after the voltage reached 3.8 V, the battery was charged at aconstant voltage of 3.8 V until the current value attenuated to 0.035mA, whereupon the capacity obtained was regarded as the chargingcapacity. Then, the battery was discharged at a constant current of0.174 mA until the final charging voltage of 2.0 V was reached.

The battery performance of the thus obtained laminate cell wasevaluated. The battery was found to have a charge capacity of 3.7 mAh, adischarge capacity of 3.7 mAh, a weight capacity density of 157 Ah/kgand a weight energy density of 502 Wh/kg at the first cycle, and adischarge capacity of 3.5 mAh, a weight capacity density of 149 Ah/kgand a weight energy density of 480 Wh/kg at the third cycle.

The polyaniline particles used in the invention have a pleatedstructure, which is now explained. The observation of the polyanilineparticles by transmission electron microscopes (TEM) reveals that thecircumference of the polyaniline particle has minute and unevenstructure composed of projections 20-300 nm high which can be referredto as a pleated structure. Such a pleated structure can be confirmed bystaining the polyaniline particles with ruthenic acid vapor to stain theparticles with the heavy metal. The pleated structure cannot be clearlyobserved when the polyaniline particles are not stained with the heavymetal.

The heavy metal staining of polyaniline powder was carried out as insuch a manner as mentioned below. Polyaniline powder in a reduced anddedoped state was put in a sample bottle container made of glass.Another bottle which was the same as the sample bottle containermentioned above was prepared, and ruthenic acid was put thereinto. Thetwo bottles were then put so that their mouths were opposite to eachother, and connected to each other by sealing the connected portion withpolyolefin film, “Parafilm” (registered trademark; stretchable andadhesive film for sealing use; available from 3M), thereby thepolyaniline powder was exposed to ruthenic aid vapor to stain the powderwith the heavy metal.

The polyaniline powder thus stained with the heavy metal was embedded inan embedding resin (epoxy resin). After the resin was cured, thinsections were prepared using a microtome, followed by subjecting to TEMobservation. FIG. 22 shows a TEM image of ruthenic acid stainedpolyaniline in a reduced and dedoped state obtained in Example 3. Theportions looking white are the embedding resin, where initially therewas cavity. The portions looking gray are the polyaniline, and theportions looking black at circumferences of the polyaniline are the“pleated structure”. It is observed that the pleated structure developedboth at the outer and inner interfaces

As set forth above, the portions of pleated structure are observed asprojections 20-300 nm high in the circumference of polyanilineparticles. The polyaniline particles thus have a large specific surfacearea because of the pleated structure. Therefore, the pleated structurethat the polyaniline particles have may be one of the reasons that thelithium secondary battery provided with a cathode comprising thepolyaniline according to the invention has a high charge/dischargeoutput performance.

In the TEM observation of the cathode sheet comprising the polyanilinepowder in a reduced and dedoped state, the conductive auxiliary agentand the polyacrylic acid mentioned in Example 3, the pleated structurecan also be observed at circumferences of the polyaniline particles.FIG. 23 is a TEM image of a section parallel to the surface of thecathode sheet of Example 3. In the TEM image, the black portions at theleft upper are composed of embedding resin where initially there wascavity. The gray portions at the left lower are phases where there arefound much polyaniline. The approximately central portions contiguous tothe gray portions where white portions and gray portions are minutelymixed together are phases composed of much of conductive auxiliary agentor carbon black, and polyacrylic acid. At the uneven portions at thecircumferences of phases composed of much polyaniline are seen thepleated structure.

The pleated structure found at polyaniline particles was also confirmedin the TEM image of the section of the cathode sheet. That is, thepresence of pleated structure was confirmed on the surface ofpolyaniline particles in the cathode.

Example 23

The production of conductive poly(o-toluidine) was carried out at ascale 10 times larger than in Example 20 to prepare conductivepoly(o-toluidine) powder having tetrafluoroborate anions as a dopant asdark green powder.

The thus obtained conductive poly(o-toluidine) powder in a doped statewas added to a 2 mol/dm³ aqueous solution of sodium hydroxide, and themixture was stirred for 30 minutes to neutralize the conductivepoly(o-toluidine), thereby dedoping the dopant, the tetrafluoroborateanions, from the poly(o-toluidine).

The thus dedoped poly(o-toluidine) was washed with water until thefiltrate became neutral, stirred and washed in acetone, subjected tofiltration using a Buchner funnel and a suction bottle, thereby thededoped poly(o-toluidine) powder was collected on a No. 2 filter paper.The dedoped poly(o-toluidine) powder was vacuum dried for 10 hours at aroom temperature to provide dedoped poly(o-toluidine) as brown powder.

The thus obtained dedoped poly(o-toluidine) powder was put in an aqueousmethanol solution of phenylhydrazine, and the resulting mixture wasstirred for 30 minutes so that the dedoped poly(o-toluidine) wasreduced, whereupon the color of the poly(o-toluidine) powder turned grayfrom brown.

The thus reduced poly(o-toluidine) powder was washed with methanol, andthen with acetone, collected by filtration, and the obtained powder wasvacuum dried at a room temperature, to provide poly(o-toluidine) powderin a reduced and dedoped state. FIG. 24 is an FT-IR spectrum of thepoly(o-toluidine) in a reduced and dedoped state (KBr disk).

0.73 g of lithium hydroxide powder was added to 100 g of 4.4% by weightconcentration aqueous solution of polyacrylic acid to lithiate the halfof the amount of the carboxylic groups of the polyacrylic acid toprepare an aqueous solution of polyacrylic acid half salt.

3.0 g of the poly(o-toluidine) in a reduced and dedoped state was mixedwith 3.0 g of conductive carbon black powder (available from DenkiKagaku Kogyo K.K.). The resulting mixture was added to 13.3 g of aqueoussolution of the polyacrylic acid half lithium salt and was dispersedtherein using a supersonic wave homogenizer to prepare a dispersion. Thedispersion was subjected to mild dispersion treatment with a highshearing force using a dispersing machine, Filmix (registered trademark)Model 40-40 (manufactured by Primix Corporation) to obtain a fluidpaste. The paste was defoamed using a vacuum bottle and a rotary pump.

The paste was coated on a sheet of etched aluminum foil for electricdouble layer capacitors (30CB; available from Hohsen Corporation) at acoating rate of 10 mm/s with a micrometer-provided doctor bladeapplicator using an automatic desk application device manufactured byTester Sangyo K.K. using a doctor blade applicator provided with amicrometer of an automatic desk application device manufactured byTester Sangyo K.K. After left standing for 45 minutes at roomtemperature, the layer of the paste on the foil was dried on a hot plateat a temperature of 100° C., to provide a composite sheet. The compositesheet thus obtained had a cathode active material which comprised thepolyacrylic acid half lithium salt, the poly(o-toluidine) in a reducedand dedoped state and conductive carbon black powder, and which wasfound to have a porosity of 72%.

A disk was punched out from the composite sheet using a punching jighaving a punching blade 15.95 mm in diameter to prepare a cathode sheet.This cathode sheet was incorporated in an HS cell in the same manner asin Example 1 to assemble a lithium secondary battery, and theperformance of the battery was evaluated in the same manner asExample 1. FIG. 25 shows the relation between the weight capacitydensity vs. the charge/discharge cycle number.

The lithium secondary battery comprising the poly(o-toluidine) in areduced and dedoped state was found to have a weight capacity densityabout 2.5 times higher in relation to the charge/discharge cycles thanthat of the lithium secondary battery comprising the conductivepoly(o-toluidine) having tetrafluoroborate anions as a dopant, as clearwhen FIG. 25 is compared with FIG. 14.

In this example in which poly(o-toluidine) in a reduced and dedopedstate was used, the weight capacity density was calculated by using onlythe weight of poly(o-toluidine) which was in a reduced and dedoped stateand had no dopant.

Comparative Example 3

(Performance of Lithium Secondary Battery Provided with a Cathode SheetComprising a Binder Comprising Styrene-Butadiene Copolymer Rubber(SBR)/-poly(N-vinylpyrrolidone) Mixture and Polyaniline in a Reduced andDedoped State)

4.8 g of polyaniline powder which was obtained in Example 3 and was in areduced and dedoped state was dry mixed with 0.6 g of conductive carbonblack (Denka Black; available from Denki Kagaku Kogyo K. K.).Separately, 0.37 g of SBR emulsion (TRD2001; having an SBR content of48% by weight; available from JSR K.K.) and 2.12 g of solution ofpoly(N-vinylpyrrolidone) (K-90W; having a content of 19.8% by weight;available from Nippon Shokubai K.K.) were mixed and stirred to prepare awhite aqueous dispersion.

The above-mentioned mixture of polyaniline powder in a reduced anddedoped state and the conductive carbon black, and then 6.9 g of ionexchanged water, were added in this order to the dispersion, followed bydispersion treatment using a supersonic wave homogenizer. The resultingdispersion was further subjected to dispersion treatment using asupersonic wave homogenizer to provide a dispersion, and then subjectedto mild dispersion treatment with a high shearing force using adispersing machine, Filmix (registered trademark) Model 40-40(manufactured by Primix Corporation) to obtain a fluid paste. The pastewas defoamed using a suction bottle and a rotary pump.

A cathode sheet was prepared by using the thus prepared binder in thesame manner as in Example 3. The cathode sheet was incorporated in an HScell to assemble a lithium secondary battery, and the performance of thebattery was evaluated. As a result, the battery was found to have aninitial weight capacity density of 100 Ah/kg when the battery wasdischarged at a rate of 0.05 C. The results of rate tests measured asthe charge/discharge current value was changed are shown in FIG. 26.

As clear from the results shown in FIG. 26, the lithium secondarybattery was found to have a weight capacity density of about 100 Ah/kg.Also in the rate test, when the discharge rate reached 5 C, almost nocapacity was taken out. Thus, as compared with the lithium secondarybattery provided with a cathode obtained by using a binder comprisingpolycarboxylic acid, the lithium secondary battery obtained in thiscomparative example was found to be remarkably inferior in ratecharacteristics.

Comparative Example 4

(Performance of Lithium Secondary Battery Provided with a CathodeComprising a Binder Comprising Polystyrene Sulfonic Acid and Polyanilinein a Reduced and Dedoped State)

7.5 g of 30% by weight solution of polystyrene sulfonic acid (availablefrom Sigma-Aldrich) was used in place of 20.4 g of aqueous solution ofpolyacrylic acid half lithium salt, and otherwise in the same manner asin Example 3, a lithium secondary battery was assembled using an HScell. The performance of the resulting battery was evaluated.

As a result, the lithium secondary battery was found to have a very lowweight capacity density. It was found that the weight capacity densityincreased gradually little by little with the charge/discharge cyclenumber; however, it was at most 2.2 mAh/g even at the 50th cycle. Thus,the lithium secondary battery provided with a cathode obtained by usinga polymer having sulfonic acid groups as a binder was found to have avery low weight capacity density and inferior in battery performance.

1. A cathode sheet for use in a nonaqueous electrolyte secondarybattery, which comprises a composite material comprising a collector anda layer of a cathode active material provided thereon, wherein the layerof a cathode active material comprises: (a) a conductive polymer and (b)at least one selected from the group consisting of a polycarboxylic acidand a metal salt of a polycarboxylic acid; and wherein the conductivepolymer is a polymer in a dedoped state or in a dedoped and reducedstate; wherein the polymer constituting the conductive polymer is atleast one selected from the group consisting of polyaniline, apolyaniline derivative, polypyrrole, a polypyrrole derivative, andpolythiophene; and wherein the polycarboxylic acid is at least oneselected from the group consisting of polyacrylic acid, polymethacrylicacid, polyvinylbenzoic acid, polyallylbenzoic acid, polymethallylbenzoicacid, polymaleic acid, polyfumaric acid, polyglutaminic acid,polyaspartic acid, alginic acid, carboxymethylcellulose, and a copolymercomprising repeating units of at least two of the polymers listedherein.
 2. The cathode sheet for use in a nonaqueous electrolytesecondary battery according to claim 1, wherein the salt of thepolycarboxylic acid is at least one selected from the group consistingof an alkali metal salt of polycarboxylic acid and an alkaline earthmetal salt of polycarboxylic acid.
 3. The cathode sheet for use in anonaqueous electrolyte secondary battery according to claim 1, which isfor use in a nonaqueous electrolyte lithium secondary battery.
 4. Thecathode sheet for use in a nonaqueous electrolyte secondary batteryaccording to claim 1, wherein the polymer constituting the conductivepolymer is at least one selected from the group consisting ofpolyaniline and a polyaniline derivative.